docs: def _Fgamma(self, x, Ep):
          """
          KAB06 Eq.58
  
          Note: Quantities are not used in this function
  
          Parameters
          ----------
          x : float
              Egamma/Eprot
          Ep : float
              Eprot [TeV]
          """
          L = np.log(Ep)
          B = 1.30 + 0.14 * L + 0.011 * L ** 2  # Eq59
          beta = (1.79 + 0.11 * L + 0.008 * L ** 2) ** -1  # Eq60
          k = (0.801 + 0.049 * L + 0.014 * L ** 2) ** -1  # Eq61
          xb = x ** beta
  
          F1 = B * (np.log(x) / x) * ((1 - xb) / (1 + k * xb * (1 - xb))) ** 4
          F2 = (
              1.0 / np.log(x)
              - (4 * beta * xb) / (1 - xb)
              - (4 * k * beta * xb * (1 - 2 * xb)) / (1 + k * xb * (1 - xb))
          )
  
          return F1 * F2